The invention relates to an oxidation furnace for the oxidative treatment of fibres, in particular for producing carbon fibres, having    a) a housing, which is gas-tight with the exception of passage regions for the carbon fibres;    b) a process chamber located in the interior of the housing;    c) at least one blowing device by means of which hot air can be blown into the process chamber;    d) at least one suction device, which sucks hot air out of the process chamber;    e) at least one ventilator, which circulates the hot air through the blowing device, the process chamber and the suction device;    f) at least one heating device located in the flow path of the hot circulated air;    g) deflection rollers, which guide the fibres in serpentine manner through the process chamber such that they lie next to one another as a carpet,            wherein the fibre carpet stretches over a respective plane between opposing deflection rollers.        
In known oxidation furnaces of this type, the different planes of the fibre carpet, which are located above one another, extend horizontally and lie parallel to the flow direction of the hot oxygen-containing air. As a result, the air flow is only involved in the heating and cooling of the fibres in its boundary layers, which are next to the fibre carpet. As a result of the parallel flow, a barrier forms at the surface of the fibres, which reduces the heat transfer. The core of the air flow is not involved in the heat transfer on account of the parallel flow. Substantial differences arise between the air entry and air exit temperature near to the fibres, which in turn leads to substantial temperature differences within the fibre carpet. The fundamental possibility of increasing the heat transfer by increasing the air speed is limited since the increasing movement of the fibres may cause them to become damaged, for example as a result of colliding with one another.
In an alternative construction of the known oxidation furnaces mentioned at the outset, the entire air flow is guided vertically through the different planes of the fibre carpet which are located above one another. This improves the heat transfer. However, the overall height is increased by the air supply system and air suction system.